Many individuals have a skin complexion which does not tan readily on exposure to sunlight. Others achieve a tan only with great discomfort and possibly adverse effects to the skin due to exposure to the sun's rays, e.g., sunburn. Yet attainment of a tan by many individuals is highly desired for cosmetic and other reasons, especially if this can be accomplished without the usual exposure to the sun, i.e., through skin tanning agents.
In other instances, individuals who tan with difficulty may desire to extend the life of a naturally acquired tan without re-exposure to the sun. Also, a skin tan may be desired when weather conditions do not permit the sun exposure necessary to acquire a tan.
Acquisition of a natural tan by exposure to the sun, however, may be almost impossible for those very light skinned persons who tend to burn rather than tan. In addition, the deleterious effects of excessive exposure to sunlight are becoming more generally recognized.
It is known in the art that an artificial tan can be achieved by applying skin tanning agents to the human skin in a suitable vehicle or base. Examples of known skin tanning agents include hydroxyaldehydes such as dihydroxyacetone; see U.S. Pat. Nos. 2,949,403 and 5,232,688. Also known as skin tanning agents are imidazole and various imidazole derivatives, such as 4-(hydroxymethylimidazole); see U.S. Pat. No. 5,252,322.
U.S. Pat. No. 2,949,403 discloses compositions of and methods of using dihydroxyacetone as a tanning agent for the human epidermis. It has been reported that dihydroxyacetone reacts with skin proteins and amino acids to elicit its skin coloring effect. Since the 1960's, several compositions using dihydroxyacetone as an active ingredient have been reported. These compositions include a topical composition containing dihydroxyacetone and various dyes such as catch powder, dogwood powder and walnut powder (the dyes are employed to offset the undesirable orange cast or hue which results from the use of dihydroxyacetone on fair skinned humans, see U.S. Pat. No. 4,708,865). These also include compositions containing dihydroxyacetone and sunscreen compounds such as octyl dimethyl PABA (e.g., U.S. Pat. Nos. 4,434,154 and 3,177,120).
Further, dihydroxyacetone has been formulated into oil-in-water emulsions, into preparations containing up to 50% alcohol which tends to dry the skin, and into "creamy bases" such as are found in hand and face lotions and creams.
U.S. Pat. No. 5,232,688 discloses compositions for self-tanning of skin which include an alpha-hydroxy substituted ketone or aldehyde such as dihydroxyacetone, a polyacrylamide and a pharmaceutically acceptable carrier.
While dihydroxyacetone has been widely employed as a skin tanning agent, commercial preparations containing dihydroxyacetone suffer from a number of drawbacks. A particular disadvantage is the physical and chemical degradation of dihydroxyacetone containing preparations over extended periods of time, for example during warehouse storage or consumer usage. Such degradation leads to discoloration, the development of unpleasant odors, and an overall loss of stability and skin-tanning efficiency. A further disadvantage of such preparations is the development of aesthetically unacceptable odors following the application of such preparations to the skin. This is thought to occur as a result of the reaction between dihydroxyacetone and the skin which results in skin tanning.
Other skin tanning agents include imidazoles, for example, see U.S. Pat. No. 5,252,322 which discloses skin tanning compositions containing imidazoles. U.S. Pat. No. 5,252,322 discloses that such compounds are believed to function by stimulating the natural processes in the skin which result in a tan. This patent further discloses several limitations to the use of imidazoles in skin tanning compositions, such as the limited solubility of such compounds in aqueous or alcoholic environments, and the possibility of skin irritation which may result when such compounds are used above certain concentrations.
Cyclodextrins have been used to encapsulate specific ingredients in cosmetic compositions; see U.S. Pat. Nos. 4,383,992, and 4,847,074. Lipari et al. in U.S. Pat. No. 4,383,992 disclose water-soluble steroid compounds formed by complexing beta-cyclodextrin with asteroid compound. Lipari et al. further disclose that various steroid compounds, including corticosteroids, androgens, anabolic steroids, estrogens and progestagens, can be used to form inclusion compounds with beta-cyclodextrin. Hatae et al. in U.S. Pat. No. 4,847,074 disclose a whitening cosmetic comprising kojic acid and cyclodextrin. Hatae et al. further disclose that such compositions have an improved stability against coloring as well as an enhanced whitening effect.
There is clearly a need for skin tanning compositions which can provide an artificial tan to the skin in a safe and nonirritating manner. There is also clearly a need for skin tanning compositions which are stable over extended periods of time, and are aesthetically pleasing to use. Further, there is a need for skin tanning compositions which efficiently tan the skin without causing unpleasant odors in the process.
It is therefore an object of the present invention to provide skin tanning compositions which are stable against physical and chemical degradation over time. It is another object of this invention to provide skin tanning compositions which color the skin without the development of unpleasant odors or skin irritation. It is a further object of this invention to provide a method for the preparation of such compositions. It is a still further object of this invention to provide a method for the use of such compositions in providing an artificial tan to human skin.
These and other objects of the present invention are achieved by incorporating effective amounts of one or more cyclodextrins and one or more skin tanning agents into cosmetic compositions. We believe this invention constitutes the first use of a cyclodextrin and a skin tanning agent such as dihydroxyacetone in a skin tanning composition.